The present invention relates to a hoisting mechanism for raising a ladle filled with liquid steel from a ladle transfer vehicle to the immersion pipes of the vacuum treatment tank of an RH degasser.
In a so-called RH degasser, liquid steel is subjected to a vacuum treatment by immersing the immersion pipes of the vacuum treatment tank into the liquid steel that is disposed in the ladle. To keep the treatment times short, the requirement exists to design the diameter of the immersion pipes as large as possible in correspondence to the ladle dimensions. In operational practice, for this purpose in one embodiment the vacuum treatment tank is lowered into the ladle, which rests upon a ladle transfer vehicle. However, this has the drawback that the vacuum treatment tank has numerous connections for the vacuum generation and for conducting treatment gasses through and for withdrawing them, so that each movement of the vacuum treatment tank means a corresponding stress upon its connections and the lines connected thereto.
Alternatively, the ladies are raised by suitable hoisting mechanisms from the ladle transfer vehicle, or also along with the transfer vehicle, and are brought to the immersion pipes of the fixedly installed vacuum treatment tank. This is accomplished by crane cable suspension means or hydraulic lifting mechanisms that ensure an exact vertical movement of the ladle, since due to the desired large immersion pipe diameter, the exact positioning of the ladle relative to IC) the immersion pipes must be ensured. Such crane cable suspension means, and also hydraulic lifting mechanisms, unfortunately require a lot of space and therefore require a correspondingly large capital investment.
Of a more economic design are hoisting mechanisms having a pivot arm that is movable by a hydraulic cylinder and is rotatable about a swivel joint during the raising or lowering movement. Such a pivot arm hoisting mechanism is known for the movement of the vacuum treatment tank of an RH degasser and can be seer, for example, in the publication “Secondary Metallurgy-Fundamentals, Processes, Applications”, publisher Stahleisen GmbH, Düsseldotf 2002, FIG. 3.2.1.5.
The drawback of such pivot hoisting mechanisms is that during the rotational movement of the pivot arm, there inevitably results not only a vertical movement, in other words a lifting movement, of the ladle that is supported by the pivot arm, but also a horizontal movement, which is dependent upon the pivot angle and the corresponding radii, along with a horizontal displacement of the vertical axis of the ladle. With the use of such a pivot lifting mechanism for bringing a ladle to the immersion pipes of a vacuum treatment tank, this kinematic would lead to a corresponding reduction of the diameter of the immersion pipes in order to take into account the horizontal movement of the ladle during its lifting or lowering movements.
It is therefore an object of the present invention for a ladle that contains liquid steel for the raising from a ladle transfer vehicle to the immersion pipes of the vacuum treatment tank of an RH degasser, to provide a lifting mechanism that operates on the basis of pivotable lifting arms, yet largely without having a horizontal movement of the ladle occur during the pivoting movement of the lifting arms.